Propeller.



A. E. MUELLER.

PROPELLER.

APPLICATION FILED AUG. 27, 1912.

150751159. Patented Nov. 11, 1913.

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WITNESSES Q 1 f1, INVENTOR f w f1? X 47% A llomey res ondin fuel econom STATES UNTT ADOLF E. MUELLER, OF LOUISVILLE KENTUCKY.

PROPELLER.

Specification of Letters Patent.

Patented Nov. 11, 1913.

Application filed. August 2'7, 1912. Serial No. 717,404.

"To all whom it may concern Be it known that I, ADoLr E. MUELLER, a citizen of the United States, residing at Louisville, in the county of Jefferson and State of Kentucky, have invented certain new and useful Improvements in Propellers, of which the following is a specification.

The object of my invention is to construct a propeller which, in comparison with a standard screw propeller intended to give approximately similar results, has a smaller diameter, a greatly increased pitch ratio, and will when driven by the same power give to a vessel an increased speed withv cor This is accom-. plished by doing away, in a great measure, with the slip loss which ordinary propellers of high pitch always show. This slip loss is largely due to the vacuum rear of the boss.

To show more clearly the nature of ,my invention some of the fundamentals of propeller design will be briefly mentioned. The basis of design is the fact that the speed of a screw per revolution depends on the pitch angle of the blade in relation to the shaft. Theoretically a propeller having a pitch angle of thirty degrees should be speedier than one in which the angle is only twent -eight degrees, and one of thirty-five degrees should travel faster than one of thirty degrees, and so on. While this is true in a certain measure, when it comes to propellers of very high pitch ratios. A propeller, being simply a small section of a two, three, or four bladed screw, suffers from the disadvantage that the pitch angle near the center does not correspond with the angle at the tip of the blade. The angle to the plane of rotation of course increases from the tip toward the base of the blade. For example, a blade of thirty degrees at the tip has a seventy de greeangle or greater at the boss when the boss is of moderate size, and while the outer edge, by reason of its small angle, will suc cessfully urge the water backward, the inner portion of the blade, which is a very abrupt angle, is practically useless because it presses the water sidewise and. churns it, expending power without any useful result. Worse than that, a vacuum is produced to the rear of the boss which has a retarding effect and causes the cavitation evidenced by the hollow observed upon the surface of the water to the rear of a rapidly revolving propeller. This cavitation increases with the pitch ratio of the propeller and is largely responsible for the loss by slip; or, better explained, the difference between the actual speed obtained and the intended speed of the pitch ratio.

' Opinions differ about the best pitch ratio. Naval vessels and ocean linersusually have propellers with pitch ratios of 1.25 to 1 (for example, a diameter of A feet and intended travel of 5 feet per revolution). A pitch ratio as high as 1.75 to l is often used on motor boats and turbine driven vessels, but it will always befound that propellers of such high pitch ratios show a higher loss formed in the this theory fails ratios.

The problems of churning and cavitation have been troublesome to naval engineers since the invention of the propeller, and three methods are in use to prevent, to a certain extent, this evil. The first is to give the blade a'pear-sh-apedform by making it gradually narrower as it approaches the amount ofhmetal will have to be added to the erosssection of the blade at this point :in order to prevent'breaking or bending. The thickening of the blade causesexpendipropulsive effect, and what is gained by re ,ducing the churning surface is largely lost {by the increased thickness.

On battle-ships and liners, in addition to the pear-shaped blade the boss is made of verylarge diameter. This is done to bring the boss out to a point on the blade where the propelling face is not so abrupt. This construction has proved to be of great advantage in cases where the number of revolutions is not greater than from 200 to 250 per minute, but it fails in cases where the speed goes up to 1,000 or more revolutions per minute. In these high speed propellers a greatly increased loss by slippage is caused by the increased size of the boss.

The third method of improvement isto make the pitch angle of the blade gradually finer as it approaches the boss. This creates an untrue or freak screw. Usually there is a drag at the base andthe economic results many inventors and has always proved a by slip than propellers of smaller pitch boss, but as a. also easily understood, a great;

ture of power in displacing water without failure. .The different parts of the blade do not work in harmony with each other, but.

easily explained in connection with the drawings which show exemplifying propellers embodying the invention.

I It is to be understod that the invention is capableo-f embodiment in difierent forms.

In the drawings :Figure l is a perspective view from a point slightly toward the bow or front end of the boss; Fig. 2 is a perspective view on a similar angle with the propeller rotating a quarter turn from the position shown in Fig. 1; Fig. 3 is a rear elevation, Fig. 4 is a view similar to Fig. 1 of a propeller provided with two apertures in each blade; Fig. 5 is a'view showing one of the blades of Figs. 1, 2 or 3 cut away closely adjacent to the boss to show the cross-sectionalform of Fig. 6 is a perspective view from the rear looking directly along the axis of one of the blade apertures of the propeller of Figs. 1,

v 2 and '8.

InFigs. 1, 2, 3, 5 and 6, reference character 1 designates the hub or boss of moderate diameter, and 2 the blades of true screw form, in this case three in number, symmetrically arranged upon the boss. Character 6 designates the propelling face of the blades and 0 designates the rearward or nonimpelling faces. Through each of the blades near the boss and in the preferred construction, directly adjoining the boss is a channel a 0. out through the blade and inclined rearv proaclnng the .area of the remaining wardly at an angle f f, Fig. 5, closely apangle 6 e of the impelling face the boss. The cross sectional parts of the blade adadjacent to V ja'cent to the hub, designated by (Z, is of gen- I Water passing through the erally triangular form of ample strength to resist bending or breaking due to leverage exerted upon the blade by water resistance. The wall 9 of channel it gives direction to channel. At the leaving edge of the blade a similarly shaped face 9' is formed. The rearward or non impellingfaces c of the blades adjacent to the boss are rounded ed to meet the faces Z) and g at sharp angles to provide easy entering and leaving edges 72/, 2', respectively.

In Fig. 4 is shown a propeller which may have an extraordinarily high pitch ratio. This also shows the blades provided with two or more channels a instead of one.

The channels a, as above stated, have a sharply defined rearward direction. They follow the boss and extend towardthe tip of the blade not more in any case than one 'esT he channels are rounded on top, as indithe blade at this point; and b cated by 70, to give free and easy passage to the discharged water. Usually a single channel is provided in each blade, as shown in Figs. 1, 2 and'3. In propellers of extraordinarily high pitch ratio or with very wide blades several channels are used to advantage as shown in Fig. 4. The purpose of these channels is to relieve the base pressure by permitting water near the boss to pass through the blades and to force this water by the power of the revolving screw in a sharply defined backward direction into the open andalso into the vacuum formed to the rear of the boss. This at once relieves back pressure and practically overcomes cavitation.

I wish to emphasize particularly the importance of the rearwardly inclined apertures or channels. A hole drilled through the blade in the plane of rotation will not work properly because the water passing through it will strike the base of the next blade abruptly, and objectionable side churning and cavitation will not be reduced. I have also found y experiment that holes of great size will show a greater loss by slip than ordinary propellers. The channels provided by my invention of proper size and angle show great reduction in side churning, cavitation and slip. The exact size of the channels depends upon the pitch ratio, the width of the blade and the speed of rotation.

A propeller of 18 inches diameter with the (in comparison with customary products) pitch ratio of 2.15 to 1 and a blade width of 10 inches, has shown in actual use the entire absence of cavitation, indicated by a perfectly flat wake, when the blade channels were made one-sixth the entire length of the blade, while anti-cavitation, indicated bya hill to the rear of the boss, appeared as soon as the openings were made largen This was the case when the screws revolved at the rate of 900 per minute. Running at a slower speed the channels had to be made larger up to about one-quarter the length of the blades to give the result mentioned. Comparing an ordinary propeller of best known form, having a diameter of 20 inches with pitch ratio of 1.7 5 to 1, with the propeller just mentioned, my propeller has shown a net gain in speed of ten percent. with the same expenditure of power and under the same conditions.

It would be impossible to use the ordinary true screw propeller as now constructed to carry out my invention by piercing the ehannels a through the blades of such a propeller, because the base of the blades when apertured would be much too weak to resist the water pressure. The blade has to be originally made very thick at the base and the material has then to be worked away from the back of the blade to make supporting members d of ample thickness and proper shape, without disturbing the true screw shape of the impelling face of the blade. The bracket-shaped or triangular connecting members at are thus produced, thus giving the construction a very high mechanical strength. It should also be emphasized that I am able by my construction to make the boss of my propeller of moderate diameter, as shown, because while the pitch of the blade increases to a very steep angle at the surface of the boss, excessive side pressure at this point is obviated by the channels a.

While I have previously referred to the advantages of my invention as a speed propeller, it should be understood that it is capable of giving improved results as a power screw when properly designed. For instance, for power use, the blades would be made somewhat wider than in a speed propeller, and there would usually be two or more channels in each blade of proper dimensions, the exact dimensions, of course, depending upon the particular use for which the wheel is intended.

By defining the propelling surfaces of my blades as having true screw form, I mean that the propelling face of the blade has a uniform pitch. Of course, with this uniform pitch the pitch angle of the face at every different distance from the boss will vary. The uniform pitch propelling surface of the blade extends from the tip to the boss, the propelling faces adjacent to the boss being indicated by characters 6. Of course, at the boss and for a short distance outward therefrom the propelling surface is interrupted by the channels 0; provided for the purpose above described.

I claim:

1. -In a marine propeller, the combination of a boss and a plurality of blades symmetrically arranged thereon, each blade having a propelling face of uniform pitch from tip to base, each blade being provided adjacent to the boss with a rearwardly inclined channel running through the blade.

2. In a marine propeller, the combination of a boss and a plurality of blades of uniform pitch symmetrically arranged thereon, the blades being of such width that they do not overlap as viewed from the end of the boss, each blade being provided with a channel running through it adjacent to the boss, the channel being inclined sharply rearwardly, the channel extending from the boss not Copies of this patent may be obtained for five cents each, by addressing the more than a quarter of the blade length toward the tip of the blade.

3. In a propeller, the combination of a boss of moderate diameter, a plurality of blades of uniform, true screw, and relatively high pitch symmetrically arranged thereon, the blades being of such width that they do not overlap when viewed from the end of the boss, each blade-being pierced by a channel adjoining the boss and directed rearwardly at a small angle to the base pitch angle of the propelling face of the blade, the blade bases connected with the boss at each side of the channel being approximately triangular in shape to give ample mechanical strength. 7

4. In a marine propeller, the combination of a boss of moderate diameter, a plurality of blades of uniform true screw pitch symmetrically arranged thereon, each blade adjacent to the boss being pierced by a channel, the axis of which is directed sharply to the rear, the channel extending radially from the boss not more than a radial length of the blade, the base portions of the blade adjacent to the aperture having impelling faces following the true screw contour of the whole blade surface, reverse faces rounded off to make sharp entering and leaving edges, other faces substantially parallel to the channel axis, whereby these base portions have a substantially triangular form to provide ample mechanical strength and free water-cutting capacity.

5. A propeller comprising a boss and a plurality of blades of uniform true-screw pitch thereon, each blade having a channel rearwardly directed passing through it at the boss and extending outward from the boss not more than one-fourth of the blade length.

6. A propeller comprising a boss and a plurality of blades thereon, each blade having an impelling face of uniform, true screw pitch from the tip to the base of the blade, each blade having a plurality of rearwardly directed channels passing through it at the boss and extending outward from the boss not more than one-fourth of the blade length.

ADOLF E. MUELLER. Witnesses:

A. M. PARKING, J 0s. N. Crown.

Commissioner of Patents,

\ Washington, I). 0.

quarter of the 

